Project Summary Kinases are valuable therapeutic targets for cancer treatment, and in recent years many small molecule kinase inhibitors have been developed and had some clinical success. A new concept in which targeting essential, but non-mutated, kinases in combination with small molecule inhibitors of driver kinases, has been exemplified by the recent approval of the combination of a BRAF and a MEK inhibitor for metastatic melanoma. Our recent research focuses on determining how cancer cells acquire invasive behavior, required for tumor expansion and metastasis, primarily by studying invadopodia, actin-rich plasma membrane protrusions that coordinate extracellular proteolysis. We used a high throughput screen to determine which kinases regulate invadopodia in melanoma cells. The top hit from our screen, TAO3, controlled invadopodia formation and function, growth in 3-dimensional matrices, and tumor extravasation and growth in vivo. We have identified small molecule inhibitors of TAO3, and solved the crystal structure of its catalytic domain, revealing unique features which could facilitate the development of selective TAO3 inhibitors. TAO3 is a promising therapeutic target in melanoma, and we hypothesize that small molecule inhibitors of TAO3 will inhibit tumor growth and invasion. This research is enabled by the collaborative activities of experts in cancer biology, biochemistry and structural biology, and medicinal chemistry. It is designed to enhance our understanding of an understudied kinase which appears to play an important role in melanoma growth. Furthermore, these studies have the potential to promote the development of a new therapeutic for melanoma and perhaps other cancers, either alone or in combination with already approved agents